To get started with GORM for Mongo you need to install the plugin into a Grails application:

grails install-plugin mongodb

With that done you need to set up a running Mongodb server. Refer to the Mongodb Quick Start guide for an explanation on how to startup a Mongo instance. Once installed starting Mongo is typically a matter of executing the following command:

MONGO_HOME/bin/mongod

With the above commands executed in a terminal window you should see output like the following appear:

If you have both the Hibernate and Mongo plugins installed then by default all classes in the grails-app/domain directory will be persisted by Hibernate and not Mongo. If you want to persist a particular domain class with Mongo then you must use the mapWith property in the domain class:

static mapWith = "mongo"

Alternatively you can persist Hibernate entities to Mongo using the special mongo scope added to all Hibernate entities: